There is nothing wrong with deaf cats! However if that other poster is right and one parent is deaf then the inheritance goes like this:

If one parent is deaf, the lowercase d, and one parent is hearing uppercase D, but carrier of deaf gene then you have a 50% chance for deaf offspring.
However, if both parents are hearing, but carriers for the deaf gene...

then you can see that only a 25% chance for deaf offspring exist.
However infection and other sickness can alter this probability in favor of deafness.